1. Field of the Invention
The present invention relates to a mold apparatus used for injection molding of molded products such as an annular packing, which is superior in pressure tightness, heat resistance, sealing characteristics, abrasion resistance, and the like, which is used in cylinders for arms, booms, adjustment, and buckets on a hydraulic power shovel and other general agricultural implements and machinery (refer to FIG. 10).
2. Background Art
In injection molded products such as annular packings made by conventional injection molding, there is a problem in that since they are molded from thermoplastic elastomer polyester (abbreviation; TPE), which is superior in heat resistance, chemical resistance, abrasion resistance and adhesive strength, the molded product is captured each time on the side of the fixed side mold (cavity) when the mold is opened, so that it cannot be completely released from the mold.
That is to say, in the conventional injection molding mold apparatus, as shown in FIGS. 11A and 11B in the mold open condition, the injection mold comprises a fixed mold member 10 and a movable mold member 30. The fixed mold member 10 shown in FIG. 11A comprises a fixed side mounting plate 12 that is fixed to four tie bars 8 (refer to FIG. 1B) by four guide pins and hooks (not shown in the figure), and a fixed side template 11 abutted against this. Moreover, on the fixed side mounting plate 12, a sprue bush 16 which aligns a nozzle (injection port) of an injection head 2 and introduces molten resin into a cavity C, is attached through a locating ring 15 for locating the mounting on the mold.
On the other hand, the movable mold member 30, as shown at the bottom of FIG. 11B, comprises: a movable mounting plate 35 which is guided by four guide pins (not shown in the figure) and moved horizontally on a floor by a drive unit (not shown in the figure), to open and close a mold member; a front pushing out plate 33 and a back pushing out plate 34 which are layer stacked on the movable mounting plate 35; a movable bush 37 that forms a concave portion of a molded product M; and a movable mold stripper 31 into which the movable bush is fitted. During injection molding the molded product M is connected to the sprue portion S by a runner R.
However, for injection molding of this kind of molded product, after injection, the mold is opened and mold release is performed. Then the movable mold stripper 31 is operated to push out the molded product, and lastly the molded product is ejected using an ejector. However, as mentioned above, since the molded product M is captured and held on the fixed side mold (cavity) member 10 side at every mold opening, hazardous mold release agents are often used, and as shown in FIG. 12A, an extension portion e which is unnecessary for the final product, is formed on the annular molded product M. Furthermore, an undercut portion u with a depth d of approximately 1.0 mm for preventing mold capture, is provided at two places for example, all around the annular molded product M, to prevent the molded product M from being captured on the side of the fixed side mold 10. That is to say, so that the molded product M remains on the movable bush 37 side at the time of mold release.
However, even if these countermeasures are taken, the situation where a molded product is still captured on the fixed (cavity) side at the time of mold release often occurs. That is to say, as described above, TPE (abbreviation) which is superior in adhesive strength, is used as the material for this kind of injection molded products. However, since for the conventional injection molding conditions, the tolerance is extremely narrow, there is the problem in that even if the molding conditions are the same for different lots (date of manufacture) for the molding material, injection molded products having the same quality and the like cannot be obtained.
Therefore, in the prior art, in the injection molding apparatus for use, at first a test piece is molded, and after molding this is immediately subjected to a predetermined mechanical process, and the processed product is annealed (for example, simply for about one hour at 120° C. approximately), and after pre-confirming faulty portions, normal molded products are produced. However, by this kind of prior art method, since molding is performed for each lot of the molding material as mentioned above, then at this point in time already 20% to 30% of defective products have occurred. Furthermore, by mechanical processing the extension portion e which is unnecessary for the final product, to separate this from the molded product at the chain line part of FIG. 12A, gives a final product such as shown in FIG. 12B. Here, for this kind of packing, a situation where traces of push out pins, parting lines and the like remain on the product surface is not permitted considering product tolerances.
Here, for molding products that have passed inspection and have been annealed (for example 12 hours at approximately 125° C.), deformation due to changes in the molecular weight of the molding material occur, so that similarly another 20% to 30% of defective products occurs.
However, for this kind of conventional injection molded products, even if the countermeasure of providing the above mentioned undercut portion is taken, it often happens that a molded product is captured on the cavity side. Therefore hazardous mold release agents are sprayed on the mold frequently (for example, at each mold opening).
Here, as this kind of mold release agent, for example, SuperFlip 7 (brand name) from Toyo Chemical Co., Ltd. that consists primarily of dimethyl ether, has been used. However not only it is expensive, but also it is hazardous, and there are problems for work safety, the environment, and the like.
That is to say, with this kind of mold release agent, because the constituent contents comprise isohexane, isopropylalcohol, silicon fluoride, dimethyl ether and the like, there is at danger such as the possibility of damage or explosion if it is left under high temperature and high humidity conditions, or thrown into water, without gas venting. Moreover since it is flammable, adequate care must be taken with fire during use. Furthermore, it is harmful if drunk by mistake or if it explodes. Moreover, highly concentrated vapor has an anesthetic action, and if inhaled, symptoms such as headache, dizziness, and vomiting appear, and in some cases it gives unconsciousness or difficulty of breathing. Moreover, it is hazardous in that it irritates the skin, eyes, mucous membrane and the like. Furthermore, the substance for forming this mold release agent can have an affect on animals, plants, birds, insects, aquatic animals, microorganisms and the like, and the substance has an influence on the environment, in that it is harmful to the natural surroundings, and water quality systems, and can have an adverse affect.
Moreover, by using this kind of hazardous mold release agent, defects such as pockmarks and peeling occur on the surface of the molded product. Furthermore, as mentioned above, because an extra undercut portion is provided on the molded product, then after injection molding, when pushing out and releasing the molded product from the mold with the movable mold stripper 31, as shown in FIG. 12C, FIG. 12D and FIG. 12E, additional defects such as turn up and deformation, easily occur on the extension portion u. Furthermore, because the sprue part S shown in FIG. 11B is similarly captured on the fixed mold side at the time of mold opening, an undercut portion u′ as shown in FIG. 11B, is provided on the sprue part S. Additionally, because the molding conditions for the conventional injection molding are extremely severe, the molded product can be deformed with only a change in the molecular weight of the molding resin. Therefore, in order to equalize the polymer structure in all molded products, an annealing process is performed over a long time at a high temperature (for example, above 100° C.).
Therefore the proportion defective of the injection molded products such as annular packings, using the conventional mold for injection molding has been extremely high at 25 to 30%.
(refer to Japanese Unexamined Patent Publication No. Hei 09-314608)